OFweek Electronic Engineering Network News: Everyone should be no stranger to resistance. I learned some of the properties and characteristics of resistance in junior high school, but the role of resistance has not been included in the scope of the system explained by the teachers. Today, the editor is incarnate Junior high school physics teacher, come to explain to everyone the knowledge about the role of resistance.

1. Introduction of resistance

Resistance (resistance), in daily life we often call it R, the unit is ohm, if you want to define the resistance, it is the size of the conductor's hindering effect on the current. The resistance is a current-limiting element, and the conductor is the current If the hindrance is large, we say that its resistance is large, and vice versa, it is said that its resistance is small. But resistance does not disappear because there is no current through the conductor. Resistance is an inherent property of a conductor. Even if there is no current flowing through the conductor, its resistance exists. If you have to give it a time limit, it should be~ Ten thousand years~~

Second, the classification of resistance

Resistance is just a general term. After a thorough understanding of it, you will know that there are many kinds of resistance, which can be divided into:

Fixed resistors, variable resistors, special resistors, RT type carbon film resistors, RJ type metal film resistors, RX type wire wound resistors, chip resistors, high-power resistors, low-power resistors.

So, what are the functions of various types of resistors? What are the applications in our daily life? To know how this matter is, please see the breakdown below~~~

Three, the role of resistance-partial pressure

When a resistor and another component such as a light bulb are connected in series in the circuit, the current flowing through the resistor and the light bulb is the same, and the sum of the respective voltages of the resistor and the light bulb is equal to the total voltage at both ends of the resistor and the light bulb as a whole. At this time, the resistor acts as a voltage divider.

Fourth, the role of resistance two-shunt

When a resistor and another component such as a bulb are in parallel in the circuit, the voltage across the resistor is the same as the voltage across the bulb, and the sum of the current flowing through the resistor and the current flowing through the bulb is equal to the total current flowing through the resistor and the bulb . At this time, the resistor acts as a shunt.

Five, the role of resistance three-impedance matching

Impedance matching refers to the process in which some methods are used to make the load impedance and the internal impedance of the excitation source adapt to each other in order to obtain a working state of maximum power output during the signal transmission process. One of its methods is to achieve it by changing the impedance. In this case, the resistor plays its role in impedance matching.

Six, the role of resistance four-filtering

In the RC charging and discharging circuit composed of resistors and capacitors in series, at first switch S is connected to point B. As shown in the figure below, there is no charge on capacitor C, and the voltage across it is zero. Then switch S is placed at point A. At this time, the power supply Start to charge the capacitor through the resistor R. When the charge on both ends of the capacitor increases to the balance of the circuit, the power supply no longer charges the capacitor. After that, the switch S is placed at point B, the capacitor begins to discharge, and the charge at both ends of the capacitor gradually decreases to zero. When the time is no longer discharging, then switch S to point A to start charging... In this infinite cycle of charging and discharging, we call the role of the resistor R as a filter.

Extended reading

The role of resistance-zero ohm resistance

There is also a special kind of resistance in fixed resistance, which is zero ohm resistance. Some children's shoes may not understand, "What is the use of resistors without resistance? It's a waste of components." In theory, this may be the case, but in actual production and life, zero-ohm resistance still has its own production. Value. Next, let the editor introduce the value of zero ohm resistance.

The use of zero-ohm resistors is often due to the need for EMC countermeasures, but there are also several reasons: zero-ohm resistors can facilitate wiring; it can make our debugging on the PCB more convenient; it is convenient to measure current consumption; It can play the role of a fuse; it can be welded on the board instead of jumpers, DIP switches, etc., to prevent users from changing settings; it can be used as an inductor or a capacitor under high-frequency signals; when the circuit parameters are uncertain, it can also be used as an inductor or capacitor. It can be replaced by a zero-ohm resistance first, and then changed after determination; it can be used to provide a smaller return path when the shortest return path is broken to reduce interference; it can effectively limit the loop current and suppress noise; it can be used as temperature compensation The device... The zero ohm resistor is so useful, my friends are surprised~~

The role of resistance-variable resistance

Variable resistors, also called potentiometers, refer to the resistance whose resistance can be changed. This variability determines its value. For example, in the analog circuits of some instrumentation equipment, sometimes there are some uncertain factors. At this time, the variability of the potentiometer is needed to adjust it to the best state. The output of some devices is constantly changing, and a potentiometer is also needed to achieve this.

The role of resistance-special resistance

Special resistors are made of semiconductor materials, and their resistance can also be changed, but unlike variable resistors, the resistance of variable resistors can be adjusted manually, while the resistance of special resistors depends on external factors. Environmental conditions. For example, the resistance of the thermistor decreases with the increase of temperature. When used in a circuit, the temperature can be judged based on its resistance and used as a thermal sensor; the resistance of a photoresistor is greatly reduced when there is light, and in the circuit It can be used as an optical switch; the resistance of the varistor changes with the change of the voltage across it, and it can play a protective role in the circuit. The protection circuit should not be damaged due to voltage fluctuations. There is also the most special type of resistor is a superconductor element, which does not generate heat when conducting electricity, and does not require a cooling system when it is made into a computer element, which can greatly reduce the size and energy consumption of the computer.

Application and development of resistance

The editor above introduced the four major functions of resistors: voltage division, shunting, impedance matching and filtering, the functions of zero-ohm resistors, variable resistors, and special resistors. Below we will come to these functions of 818 resistors in real life. App~

① The shunt function of resistance is often used in various circuits to distribute current;

② The voltage divider effect of resistors is often used in the volume adjustment circuit of radios and amplifiers, the bias circuit of the semiconductor tube operating point and the step-down circuit, and on the USB to serial port line, two resistors are often used to divide the voltage to get 3.3 V or 2.8V serial port;

③ The filtering effect of resistors is often used in integrating circuits, differential circuits, decoupling circuits, timing circuits, etc.;

④ The impedance matching effect of resistance is often used on transmission lines;

⑤ The thermistor can be used as a thermal sensor, and the photoresistor can be used as an optical switch;

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Today, the resistance system has been developed so large that it is used as a basic component in various electronic products, but it has not stopped, and is still moving towards perfection. I believe that resistance will further reduce its size in the near future. , Improve performance, reduce prices, will eliminate some of the outdated and add some fresh elements, when the resistance of the high-end atmosphere rises another level, the editor will take everyone to learn together~~